Defoaming agent, lubricating oil composition containing defoaming agent, and machine using lubricating oil composition

The lubricating oil composition according to claim 13, wherein the polymerizable monomer (1) is a compound represented by General Formula (1-1) below:

• in General Formula (1-1) above,
• R11 is a C1-6 alkyl group or a group represented by —OSi(R17)3 (R17s are each independently a C1-3 alkyl group),
• R12 is a C1-6 alkyl group or a group represented by —OSi(R18)3 (R18s are each independently a C1-3 alkyl group),
• R13 is a C1-6 alkyl group,
• R14 is a C1-6 alkyl group,
• R15 is a C1-6 alkyl group,
• R16 is a hydrogen atom or a methyl group,
• L1 is a divalent organic group, and
• n is an integer of 0 or more.

A lubricating oil composition comprising:

• a lubricating oil base oil;
• and
• a defoaming agent,
• the defoaming agent being a polymer with a polymerizable monomer (1) having a silicone chain-containing functional group and a polymerizable monomer (2) having a polyoxyalkylene chain-containing functional group as a compound represented by Formula (2-1) below as polymerization components:
• in General Formula (2-1) above,
• R21 is a hydrogen atom, a C1-30 alkyl group, or a phenyl group,
• R22 is a hydrogen atom or a methyl group,
• n is an integer in a range of 1 to 4,
• m is an integer in a range of 1 to 4, and
• p and q are each independently an integer in a range of 0 to 200 and satisfy p+q≥1.